Suckerfish, or remora fish, are notorious hitchhikers. They suck on all manner of larger marine animals, such as sharks, dolphins, sea turtles and stingrays, and allow themselves to be transported princess-like. Even divers and boats are joined by these fish, which apparently have no qualms about invading the personal space of their hosts.
You may also want to read about Dall’s porpoise.
Hitchhiking remora fish
Hitchhiking gives a remora several advantages. It does not have to swim itself, which saves a lot of energy, and it also gets a free meal. The sucker fish eats parasites from its host’s skin or devours the leftovers of its careless eater. Most hosts also unintentionally provide safety. A predator targeting a remora will think three times before attacking if its prey is attached to a shark. And if there are several suckerfish on the same host, the hitchhikers may yet come across a suitable mate.
And what’s in it for the host? Well, not too much. Removing parasites is a good thing, but it stops there. Dragging a remora along provides some extra resistance. With a single streamlined sucker fish this is negligible, but with dozens of lifters it ticks up. Also, the “sucking spot” may cause irritation.
Although most hosts tolerate the uninvited hitchhikers, as seen in many nature films, some prefer to get rid of them. But that just doesn’t happen. To illustrate, makos (mackerel sharks) are the sprinters among sharks. They can reach up to 70 kilometers per hour. An attached suckerfish just stays attached and gets somewhere.
The host only gets rid of the unwilling suckerfish by scraping vigorously along rocks or the bottom, or by jumping out of the water and falling with a crash to the surface. Or if the suckerfish gets fed up with it itself and switches to other transportation.
In some regions, remoras are used to catch sea turtles, for example. A fisherman ties a rope around the sucker fish’s tail and then lets it do its thing. Once the fish has attached itself, it is brought in with host and all. Remora fish are therefore sometimes called “fishing fish. It once again underscores their exceptional tenacity.
An oval suction cup on top of their head provides a firm anchorage for suckerfish. The suction cup is a converted dorsal fin and consists of rows of movable and toothed lamellae surrounded by a soft, fleshy rim. To attach itself, a remora presses against its host. Water is removed from the sucker, partly because the lamellae are pushed down and force water out.
This creates negative pressure, which creates a suction, and the remora is anchored. To stay anchored at high swimming speeds of the host, the suckerfish parks the toothed lamellae against the host’s skin. That provides enough friction with the host’s often rough skin to stay anchored.
Our suction cups, on the other hand, often have problems with rough surfaces and release quickly. Therefore, engineers built a suction cup inspired by the remora. Essential here are the soft edge that conforms to the rough surface, providing a virtually air or watertight seal, and the serrated fins that “brace” against the surface.